Industrial controllers are special-purpose computers utilized for controlling industrial processes, manufacturing equipment, and other factory automation, such as data collection or networked systems. In accordance with a control program, the industrial controller, having an associated processor (or processors), measures one or more process variables or inputs reflecting the status of a controlled system, and changes outputs effecting control of such system. The inputs and outputs may be binary, (e.g., on or off), as well as analog inputs and outputs assuming a continuous range of values. Control programs may be executed in a series of execution cycles with batch processing capabilities.
Measured inputs received from such systems and the outputs transmitted by the systems generally pass through one or more input/output (I/O) modules. These I/O modules serve as an electrical interface to the controller and may be located proximate or remote from the controller including remote network interfaces to associated systems. Inputs and outputs may be recorded in an I/O table in processor memory, wherein input values may be asynchronously read from one or more input modules and output values written to the I/O table for subsequent communication to the control system by specialized communications circuitry (e.g., back plane interface, communications module). Output modules may interface directly with one or more control elements, by receiving an output from the I/O table to control a device such as a motor, valve, solenoid, amplifier, and the like.
Various control modules of the industrial controller may be spatially distributed along a common communication link in several racks. Certain I/O modules may thus be located in close proximity to a portion of the control equipment, and away from the remainder of the controller. Data is communicated with these remote modules over a common communication link, or network, wherein modules on the network communicate via a standard communications protocol. Many industrial controllers can communicate via network technologies such as Ethernet (e.g., IEEE802.3, TCP/IP, UDP, EtherNet/IP, and so forth), ControlNet®, DeviceNet® or other network protocols (Foundation Fieldbus (H1 and Fast Ethernet) Modbus TCP, Profibus) and also communicate to higher level computing systems. Industrial controllers utilize the aforementioned technologies along with other technology to control multiple applications ranging from complex and highly distributed to more traditional and repetitious applications.
At the core of the industrial control system, is a logic processor such as a Programmable Logic Controller (PLC) or PC-based controller. Programmable Logic Controllers for instance, are programmed by systems designers to operate manufacturing processes via user-designed logic programs or user programs. The user programs are stored in memory and generally executed by the PLC in a sequential manner although instruction jumping, looping and interrupt routines, for example, are also common. Associated with the user program are a plurality of memory elements or variables that provide dynamics to PLC operations and programs. These variables can be user-defined and can be defined as bits, bytes, words, integers, floating point numbers, timers, counters and/or other data types to name but a few examples.
As PLC's have evolved however, the associated logic programs have become ever more sophisticated and complex. In many cases, these programs include valuable intellectual property that must be protected from those who do not have appropriate credentials for accessing, removing, and/or modifying such programs. In addition, there may be safety concerns if programs are improperly modified by unauthorized personnel or modified at an inappropriate time (e.g., unpredictable machine operation caused by changed, added, conflicting or removed logic elements). Also, relating to these security concerns, the manner in which PLC program and data files are stored can be problematic. For example, common database servers and associated software are generally not adapted in an off-the-shelf manner to accommodate the types of images that are created and operated upon by a PLC. In one common database application, when changes are made to a stored file on the database, the changes are stored in a delta file which merely logs the changes in a separate file from a base file that has been previously stored. While the delta file may be useful for enabling reconstruction of the base file having the desired changes for such file types as text files, this technique is not suitable for images that drive PLC operations since PLC images are compiled and stored as an integrated whole.